The Up/Down swipes work just like skipping back/forward by chapter marks on earlier Kindles.

Not entirely. Previous Kindles (I don't know about K4) would (normally) only visit 'top level' nav points defined in the NCX with the 5way. Kindle Touch visits all of the nav points, regardless of 'level'. I like it!

Publishers were advised to 'flatten' their NCX hierarchy as part of converting ePub files. But many ignore that advice, rendering their books less navigable than they might be on Kindle. But on KT it no longer matters if they do or don't.

I hope (probably in vain) that Amazon adds an NCX navigator as part of KF8 upgrade. Kindle Previewer has always had one and it is much better than using the hyperlinked TOC that we're otherwise stuck with.